Fiber-optic couplers are known in the art, and are employed for optically coupling fiber-optic components. Fiber-optic couplers are constructed in various methods, such as fused bi-conical couplers, dichroic couplers (i.e., Wavelength Division Multiplexing—WDM), fused-end couplers, side couplers and the like. Fiber-optic couplers have various configurations, such as a Y-shaped coupler (i.e., fusing two fiber-optic cables into a single cable—2X1), an X-shaped coupler (2X2), and the like.
Light losses in the coupler area are minimized, and an efficient coupling is achieved, by surrounding the coupler with materials having refractive index smaller than that of the coupler (i.e., lower than that of each of the fibers of the coupler). Low refractive index encapsulation of the fiber-optic coupler further protects the fiber-optic coupler from impurities (e.g., dust particles) and humidity. Generally, the low refractive index encapsulation is optically transparent for light of the range of wavelengths of the coupled fibers.
High power fiber-optics include fiber-optic components (e.g., fibers and couplers) which transmit optical power exceeding the order of 1 Watt. High power fiber-optic couplers are exposed to thermal effects which degrade coupling efficiency and might even damage the components of the coupler. A known approach to the problem of thermal effects is encasing the coupler in a thermally conductive packaging, and coupling the package with a heat-sink. The heat-sink evacuates excess heat from the coupler packaging to the surrounding environment.
There are several mechanisms which generate heat at the coupler area. A first mechanism of heat generation is the absorption of light in impurities within the coupler, and the transformation of the absorbed light into heat. This mechanism is minimized by employing optically transparent coupler encapsulation and adhesives. A second mechanism is the absorption of light escaping from the coupler in the metal coupler packaging. The efficiency of most couplers ranges between 85%-95% (i.e., the light loss ranges between 5%-15%, which might be transformed into heat by absorption in the metal packaging).
U.S. Pat. No. 5,822,482 issued to Atkeinsson et al., and entitled “Fiber Optic Coupler Package with Strain Relief and Packaging Method”, is directed to a protective packaging for a fiber optic coupler. A fiber optic coupler protective body is a rectangular block of quartz, which includes a longitudinal channel. The fiber optic coupler is coupled with the protective body by an adhesive, such that the fiber optic coupler is suspended within the longitudinal channel of the protective body.
U.S. Pat. No. 6,167,176 issued to Belt and entitled “Fiber Optic Coupler”, is directed to a fiber optic coupler. The fiber optic coupler is bonded to a substrate of a clamshell shaped Neoceram sleeve. The Neoceram sleeve forms a primary chamber, and is closed at both ends with thixotropic paste. A secondary Invar (FeNi36) tube is positioned over the primary chamber, and both its ends are filled with epoxy. The Invar tube is further encapsulated within thixotropic paste. A tertiary tube is positioned over the secondary tube and both its ends are filled with epoxy. It is noted that, Invar is an opaque nickel steel alloy which absorbs light and transforms it into heat.
U.S. Pat. No. 6,788,852 issued to Xu and entitled “Double Tube Fiber Coupler Package”, is directed to a fiber optic coupler package. The package includes an inner cylindrical sleeve made from quartz and an outer cylinder made of Invar. The thermal expansion coefficient of the Invar cylinder is substantially zero. The package provides moisture, anti-vibration, impact, corrosion, and thermal expansion protection.